GPS (Global Positioning System) has been known as a conventional positioning system. A satellite (hereinafter referred to as a “GPS satellite”) transmitting a signal used for GPS (hereinafter referred to as a “GPS signal”) flies at an altitude of about 20,000 km from the ground. By receiving and demodulating a signal emitted from the GPS satellite, a user can measure the distance between the GPS satellite and the user. Therefore, if there is no obstacle between the ground and the GPS satellite, positioning is possible using the signal emitted from the GPS satellite. Assume, however, use of the UPS in an urban area. It may often the case that the signal emitted from the GPS satellite cannot be received by a positional information providing apparatus of the user, hindered by high buildings standing in large numbers. Further, diffraction or reflection of the signal by a building may cause an error in the distance measurement using the signal and, as a result, positioning accuracy is often degraded.
Though a technique has been known to receive in a room a weak GPS signal that has passed through a wall or roof, state of reception is unstable and positioning accuracy is low.
In the foregoing, positioning using GPS has been described by way of example. The phenomenon described above, however, is common to positioning systems using satellites in general. The satellite positioning system is not limited to GPS, and it may include systems such as GLONASS (GLObal Navigation Satellite System) of Russian Federation and Galileo of Europe.
Technique related to provision of positional information is disclosed, for example, in Japanese Patent Laying-Open No. 2006-67086 (Patent Document 1).
Patent Document 1: Japanese Patent Laying-Open No. 2006-67086